The fire, which officials believe may have been started by a discarded cigarette butt, broke out at 6:30 a.m. local time (1330 GMT) on Thursday, less than 10 miles (16 km) from the Pacific coast.

Since Friday morning, the fire grew from 10,000 acres to 28,000 acres (11,300 hectares), reaching within a short distance of the Pacific Coast in some places, forcing authorities to close several miles of the Pacific Coast Highway.

The Ventura County Fire Department (VCFD) said late Friday that the blaze was just 20 percent contained. Fleets of water-dropping helicopters and planes dropping loads of fire-retardant chemicals ended their operations for the night. However, ground crews continued battling the blaze, the department said.

Since the blaze started, it has burned through more than 43 square miles (111 square kilometres) of land, and fire managers said they expected it would take another week to fully contain the blaze.

Typically, California has fires later in the year, but strong Santa Ana winds and high temperatures have triggered a series of brushfires around the state this week, marking an early start to a California fire season.

"We're seeing fires burning like we usually see in late summer, at the height of the fire season, and it's only May," VCFD spokesman Tom Kruschke said.

Some 4,000 homes were considered threatened, with evacuations ordered for about a quarter of those residences, the VCFD said. Fire officials said that 25 outbuildings were destroyed. But no residential structures were destroyed and no injuries had been reported.

At the Point Mugu US Naval Air Station on the coast, non-essential personnel were ordered to stay home for a second day as flames infringed on the far western end of the base, spokeswoman Kimberly Gearhart said.

California State University at Channel Islands remained closed for a second day Friday, "due to the (fire) and heavy smoke drifting onto the campus."

hc/jr (Reuters, AFP)